The present invention relates to a method and an apparatus for evaporative cooling of tools of glass-forming machines, for instance plungers and molds, with a cooling liquid.
Known method and apparatus of this type are described in an article "Methoden der Formenkuhlung an Glasverarbeitungsmaschinen" ("Methods for Cooling of Molds in Glass-forming Machines") by Rudolf Wille, published in the magazin No. 7 "Konstruktion und Betrieb von Glasverarbeitungsmaschinen" ("Construction and Operation of Glass-forming Machines"), published by the Deutsche Glastechnische Gesellschaft (German Society for Glass Technique), Frankfurt am Main, 1961, pages 35 - 43. There a plurality of nipples, into which cooling water is fed in the form of drops, are screwed locally into the outer wall of the mold. This known way of cooling a mold has many disadvantages. The heat sinks, i.e., the nipples, are stationarily arranged with regard to the mold surface. The diameter of each of the nipples is necessarily small and a mold provided with a plurality of such nipples is relatively expensive. Such molds have to have a relatively great wall thickness in order to permit a threading connection of the nipples and in order to obtain, in view of the small size of the heat sinks, by means of increased wall thickness a sufficient temperature distribution over the entire mold surface. While it is possible to provide a relatively great number of nipples per surface unit, such an arrangement will evidently be rather expensive. The known mold has relatively large dimensions, due to the necessary great wall thickness, the nipples threadingly connected thereto, and the necessary feed conduits for feeding cooling fluid to the nipples, which is especially detrimental when for the mounting of the mold, especially in molds for small hollow glass bottles, only limited surface areas are available. This particularly holds for conditions where double gob molds are operated.*) An additional disadvantage of this known arrangement is that water will collect at the bottom of the nipples so that evaporation of the liquid will occur beneath the liquid level and therefore under difficult conditions. FNT *) Caused by the design of the production machines, double gob molds are arranged so close together that no nipples can be located in an area which needs cooling most.
At sufficiently large overheating of the liquid the danger of film evaporation with a greatly reduced heat-transfer coefficient exists (see the above referred Wille article, page 39, picture 8). There exists further the difficulty to optimize the spatial arrangement of the heat sinks, since the heat sinks cannot be in any desired manner distributed over the surface of the mold. A cooling of the mold bottom in a divided mold is not provided. In addition, there is no possibility to influence at these known heat sinks the amount of the heat transfer.
According to another known method and apparatus (Austrian Pat. No. 24,927) an adjustable amount of cooling liquid is dripped or squirted into the hollow wall of the mold. The thus formed water vapor passes through the cavity formed in the mold wall to cool the latter. This method has the disadvantage that the water fed into the mold, will impinge only onto a relatively small area of the mold surface. A further disadvantage is the fact that the temperature of the mold surface is so high that a vapor cushion develops beneath the infed water. As already explained hereinabove in connection with the Wille article, this cushion develops because the high temperature difference between mold surface and water prevents the desirable so-called bubble type evaporation. What actually occurs is the so-called film evaporation, i.e., the formation of a continuous vapor film between mold surface and water (the Leidenfrost phenomenon), which yields a much lower heat transfer coefficient than with bubble evaporation. The described cushion of the vapor film prevents the desirable and necessarily high heat extraction from the mold. A cooling of the remainder of the mold wall by convecting heat transfer by means of water vapor is, due to the small amount of available vapor volume, not obtainable and therefore an essential improvement of the cooling of the remainder of the mold wall cannot be expected. A substantially uniform temperature of the mold surface facing the glass is not obtainable with this known cooling method, neither is it possible to obtain sometimes desired temperature profiles on the surface to be cooled. In addition the mold wall has to be hollow and relatively thick, and requires therefore a relatively large space, which, especially in modern compact automatic glass forming machines, is not available.
It is further known from the German Auslegeschrift 2,150,193 to spray a cooling liquid directly onto the tool surface to be cooled, which may be profiled.